Producing hydrocarbons from a subterranean well often requires the separation of the desired hydrocarbons, either in liquid or gaseous form, from unwanted liquids, e.g., water, located within the well and mixed with the desired hydrocarbons. If there is sufficient gas reservoir pressure and flow within the well, the unwanted liquids can be progressively removed from the well by the hydrocarbon gas flow, and thereafter separated from the desired hydrocarbons at the surface. However, in lower pressure gas wells, the initial reservoir pressure may be insufficient to allow the unwanted liquids to be lifted to the surface along with the desired hydrocarbons, or the reservoir pressure may decay over time such that, while initially sufficient, the pressure decreases over time until it is insufficient to lift both the hydrocarbons and undesired liquid to the surface. In these cases, artificial lift methods of assisting the removal of the fluids are required.
More particularly, in gas wells where the reservoir pressure is insufficient to carry the unwanted liquids to the surface along with the gas, the unwanted liquids will not be carried up the wellbore by the gas, but will rather gather in the well bore. The back pressure created by this liquid column will reduce and may block the flow of gas to the surface, thereby completely preventing any gas production from the well. Even in cases where the initial reservoir gas pressure is sufficiently high to remove the unwanted liquids, this pressure will decay over time and the wells will reach a point where economic production is not possible without a system for assisting in the removal of the unwanted liquids from the well bore, otherwise known as deliquification. Deliquification by artificial lift is therefore a requirement in most gas producing wells. A very similar situation exists in low pressure oil wells, where the well pressure may be insufficient to lift the produced oil to the surface.
A number of methods are known for assisting the lift of liquids in hydrocarbon wells to the surface, including, but not limited to, reciprocating rod pumps, submersible electric pumps, progressive cavity pumps, plungers and gas lifts. However, in some cases, for example in gas producing shales where permeability is low, it is necessary to drill these wells with deviated well sections (i.e., sections extending at an angle from the main, substantially vertical, bore) using horizontal drilling technology which exposes greater amounts of the producing formation, thereby making the well commercially viable. The length of the horizontal section of such wells can make artificial lift of the liquids both expensive and technically difficult using currently available technology. For example, reciprocating rod pumps and large electrical pumps cannot easily be placed, driven, or otherwise operated in a long horizontal, or substantially horizontal, section of a well bore, while devices such as plungers generally fall using gravity only, and cannot therefore get to the end of a horizontal section. The pump may have to be large to overcome the entire static pressure head within the system.